Preterm birth is a major public health problem in the USA. The single most important factor in predicting preterm birth is premature cervical dilatation. Our knowledge on the mechanism of dilatation of the human cervix in labor is extremely limited, partly due to the lack of accessibility of the cervix for direct biochemical experimentation. Alternative approaches utilizing biopsies of the human lower uterine segment (LUS) and guinea pig model will be used to test the hypothesis that for the cervix to dilate in labor it must invoke activation of type I collagen degradation, the main structural protein of the cervix, in the extracellular matrix by a significant increase in interstitial collagenase activity, the rate limiting enzyme in fibrillar collagen degradation. This hypothesis will be tested under 3 conditions: 1. Physiological state- term labor: biopsies of LUS will be obtained from women at term (37-42 wks) in labor and matched control group not in labor. 2. Pathological state-preterm labor: biopsies of LUS will be obtained from women in preterm labor (26-36 wks) and matched control group not in labor. 3. Pharmacological state-in vitro: Agents that are known or have the potential to dilate the cervix such as prostaglandins (PGE2 and PGF2a), interleukin-1 beta and relaxin will be tested in organ culture of cervices of 50 day pregnant guinea pigs. The specific aims are: 1. To determine the effects of labor on the gene expression of interstitial collagenase, TIMP1 and TIMP2 and the level of degradation of type I collagen in the extracellular matrix by interstitial collagenase (TC(A), TC(B) collagen fragments) in biopsies of LUS in the four groups of women described above at full term and preterm gestation with and without labor. 2. To determine the effects of PGF2alpha:, PGE2, hrIL-1 beta and hr Relaxin in cervical cultures of 50 day pregnant guinea pigs on type I collagen degradation by interstitial collagenase. The protective effect of progesterone (10[-4]M) on collagen degradation will also be determined. 3. To isolate, characterize and determine the primary structure(s) of cervical epithelial cell derived peptide(s) (6 kDa) that stimulate(s) cervical stromal cell collagenase biosynthesis by using guinea pig cervical stromal and epithelial cells in culture HPLG, electrophoresis and microsequencing. Identification of this/these factors will allow for future studies to define its/their role in dilatation of the cervix in labor.